Endoscopic procedures are steadily replacing more traditional invasive surgical procedures in contemporary medical practice. During traditional surgical procedures, incisions are required to be sufficiently large to allow direct visual observation of tissues and organs and to allow manipulation of the tissue and organs by a surgeons hands and traditional surgical tools. During an endoscopic procedure, only very small incisions or punctures are made through which catheters and a small diameter endoscope tube are inserted. Light for illumination, and a return visual image of tissues and organs, are conducted through the tube by optical-fibers. Light for illumination is provided by an endoscope light source and is conducted to the endoscope tube through a light conducting conduit, typically a flexible optical-fibre cable.
Generally, as may be seen in FIG. 1, a light source end of an optical-fibre cable 10 is fitted with a metal sheath 20 having locating shoulder 21. Coupling devices of endoscope light sources of the prior art typically include fitting 14, with port 18 sized to receive sheath 20 in a sliding fit, attached to light source cabinet wall 16. Sheath 20 is inserted into light source port 18 until shoulder 21 contacts cooperating shoulder 12 within fitting 14 and sheath 20 is positioned with sheath end 22 protruding from the back of the fitting. Sheath 20 is retained in this position by tightening set screw 15. In this position, light from a light source lamp is focused by lens 17 upon exposed ends of light conducting fibers of cable 10 at protruding end 22 of cable sheath 20 to provide illumination.
In endoscopic light sources of the prior art, extreme heating of the end portion of the sheath and cable occurs during illumination. Adverse effects of this heating of the cable most notably include discoloration and loss of light conducting efficiency at the end portion of the cable over time. This deterioration in cable performance may result from breakdown and scorching of cable bonding materials and optical fiber coatings of the cable. The light source end of the optical-fibre cable is customarily repolished from time to time in a effort to restore performance until the cable must finally be discarded. Extreme heating of the cable and sheath end may also present a burn hazard to operating-room personnel when a cable is removed from a light source without allowing a sufficient cooling time with the light source lamp turned off.
Heating of the light source cable end occurs for a number of reasons. Less efficient light conducting materials in the cable, including bonding and fiber coating materials, convert impinging light energy into heat energy. Focusing of the lamp beam is not perfect, and, consequently, a portion of the focused beam may impinge upon the opaque sheath wall where it contributes to heating of the end portion of the sheath. Electro-magnetic radiation from the light source lamp outside the visible spectrum may also impinge upon the end portion of the sheath, further contributing to heat build up.
Attempts have been made to reduce heating of the cable end portion but they have proved ineffective or cumbersome. One light source of the prior art has utilized an air pump and nozzle to direct a stream of cooling air upon the cable end. While this method of cooling has proved effective in reducing heating of the cable end and mitigating deterioration of cable performance over time due to heating, it increases the complexity, weight, size and number of mechanical components of the light source apparatus.